This invention relates to a pump assembly including a pump which is externally controllable so that the volume and/or pressure of the fluid to be transported by the pump can be varied with time in a desired manner. More specifically, this invention relates to an externally controllable pump for pumping blood.
Pumps which are externally controllable to vary with time the volume and/or pressure of the fluid passing therethrough are known. For example, such pumps are utilized for supplying fuel to internal combustion motors. In these prior art pump assemblies, however, the control of the volume and/or pressure with respect to time customarily occurs only by mechanical means and, usually, control is possible only in response to the RPM of an internal combustion motor.
There are many instances, however, in which a particular supply or pressure curve is desired during the working cycle of the pump. For example, a blood pump should imitate the pumping "characteristics" of the natural heart as precisely as possible, especially if it is working in conjunction with an artificial heart. Moreover, such pump assemblies are desired for, among other things, artificial respiration devices, for dialyzers and for heart-lung machines. In addition, such pumps are also useful in different technological areas.
In order to achieve a desired timewise variance of the volume and/or pressure within each cycle of the pump, i.e., in order to achieve a particular pumping characteristic when using a pump assembly of the kind mentioned above, the pump is coupled to a programmable data memory unit which is programmed to correspond to the desired variation with time of the volume and/or pressure and which can be scanned at a controllable time-rate.
The desired pumping characteristic can be put into a programmable memory unit which, for example, can be a semi-conductor data storage or a number of sequentially addressable resistors whose values correspond to the program. In the latter case the resistors are sequentially addressable by a demultiplexer to which can be fed the time-sequential output signals of a binary counter, so that the pump conveys the fluid to be transported in accordance with the stored program during each operating cycle. For the purpose of controlling a blood pump, the pumping characteristics of the heart can be very precisely imitated in this way so that otherwise possible damage to the organism can be avoided.
The pump utilized in the present invention can be hydraulically driven and can be connected to a servo valve which supplies hydraulic fluid to the pump in accordance with the stored program. However, it is also possible to power the pump by a stepping motor which is itself controllable in accordance with the stored program or in the alternative, the pump may be a piston-type pump having a piston which is driven by a linear motor in accordance with a stored program.
In order to be able to read out the program in the memory unit in the desired time sequence and to utilize the program instructions for controlling the pump, a controllable clock generator is provided which is connected to the data storage through an address counter for the purpose of sequentially scanning of stored program. In order to achieve the desired time sequence, special control signals can be fed to the clock generator. The control signals can be derived, for example, from measured data. In a blood pump, the measured data can be obtained from the oxygen content of the blood and from the atrial pressure of the artificial heart so that the temporal sequencing for reading out the stored program can be appropriately established and, if necessary, modified.
If desired, the memory can also contain several programs for the volume-time and/or pressure-time characteristic of the pump simultaneously, and the pump system can be switched to the desired program by a program selector. In this case, the switch-over from one program to another in the memory can be made to depend on the output signal of the memory, for example, when the signal output passes through the value zero, so as to ensure continuity of blood circulation.
If a hydraulically driven pump having a servo-valve connected thereto is employed, a digital-to-analog converter can be connected between the data storage and the servo valve so that the output of the digital-to-analog converter provides the control signals for operating the servo valve. In addition, the output signal of the digital-to-analog converter can be fed to a maximum value decoder for generating a signal when the maximum amplitude of the output signal of the analog-to-digital converter occurs. That signal is used to control the clock generator for systolic or diastolic generation. Therefore, the clock generator generates two different clock-trains for addressing the memory. Such a signal is especially advantageous if the pump assembly is used, together with a blood pump, for supporting the natural blood circulation, for, in that case, the signal can serve to adapt the operation of the two pump mechanisms.